1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor wafer, a semiconductor manufacturing apparatus, and a semiconductor device. It especially relates to improvements in adaptability to the expansion or reduction of the scale of production at a low cost.
2. Description of the Background Art
A semiconductor wafer conventionally used in the semiconductor process is a circular wafer S0 having a generally round plane form as shown in FIG. 41. In the circular wafer S0, a matrix of many rectangular semiconductor chips are formed in a chip region 150. As one of means for saving the cost of manufacturing a semiconductor, the diameter of the circular wafer S0 is being increased as shown in FIG. 41. This is based on a simple hypothesis that whether the circular wafer S0 has a large diameter or not makes little difference in the cost of processing a single circular wafer S0.
The circular wafer S0 is, as shown in FIG. 42, obtained by first forming a generally cylindrical semiconductor ingot 152 and then slicing it along planes perpendicular to the central axis. To increase the diameter of the circular wafer S0, therefore, the diameter of the semiconductor ingot 152 must be increased. Increasing the diameter of the single crystalline semiconductor ingot 152 is, however, not a ready technique so that a new developing cost is required.
In addition, with the increase in the diameter of the circular wafer S0, a semiconductor manufacturing apparatus 155 for manufacturing a semiconductor device using the circular wafer S0 must be modified to the apparatus 156 suitable for a larger-diameter circular wafer S0, as shown in FIG. 43. Such modification of the semiconductor manufacturing apparatus needs to be made through the entire semiconductor manufacturing process.
Especially, to uniformly process a circular wafer S0 having a larger surface area, it is necessary to improve uniformity in density of plasma or reaction gas, which requires developments of new technologies. As a result, new introduction of a more expensive semiconductor manufacturing apparatus, i.e., larger scale of capital investments, is required.
That is, the processing cost of a single circular wafer S0 is not the same as hypothesized but tends to rise with the increase in diameter. This results in enormous costs required for the capital investments with the increase in diameter, which cannot be covered only by a semiconductor maker.
As the number of semiconductor chips per circular wafer S0 increases with the increase in diameter, the number of semiconductor devices supplied for markets increases. If expansion of a semiconductor chip market fails to measure up to projections, the price of a semiconductor chip will fall due to a balance between supply and demand. Consequently, it could happen that the capital investments made for the increase in the diameter of the circular wafer S0 cannot be recovered. That is, the increase in diameter is attended with risk.
Moreover, recent development of the semiconductor manufacturing technique allows integration of an enormous number of circuit elements into a single semiconductor chip, which had been unthinkable before. This is followed by a move afoot to form a highly integrated circuit by combining various circuit components (referred to as "micro cells" or "IP (Intellectual Property)"), each composed of a plurality of circuit elements and performing a certain function.
A principal purpose of the conventional semiconductor device manufacturing technique is mass production of only a few kinds. A new "IP" age wherein an integrated circuit is formed of IPs, however, requires either flexible manufacturing system or mass production of multi kinds. In this "IP" age, even a DRAM which itself is a large scale integrated circuit is handled as a single IP. Conventional increase in the diameter of the circular wafer S0 to make a profit has been made on the understanding of the mass production of only a few kinds, but if things continue to be the way they are under the new condition of the flexible manufacturing system, it is not easy to ensure profits.